1. Field of the Invention
The present invention is in the field of valve constructions and is more particularly directed to a three way valve shiftable between three conditions of operation, namely, a condition in which air from a load (pneumatically operated device) is vented to an exhaust port, a condition in which air from a supply port is connected to the load, and an intermediate condition in which all flow through the valve is blocked.
2. The Prior Art
Numerous valve constructions are currently available which are adapted by manual or automatic operation selectively to vent a load to atmosphere or, alternatively, by actuation of the valve, to connect the load to a source of air under pressure.
Typically such valves include a shiftable plunger, a supply port, an exhaust port or passage, and a load port. In the normal operative condition the load is vented through the exhaust port. When such valves are actuated by shifting the plunger, the components move progressively to an intermediate position whereat all ports are sealed, and then to a final position whereat the supply pressure is connected to the load.
Movements from the described normal to the charging position in valve devices heretofore known have embodied two distinct actions which have greatly reduced the useful life cycle of the valve. In typical constructions, the plunger carries an O-ring which, in the course of movement of the plunger from the normal to the charging position is caused to enter into a bore or channel to effect a seal, whereby the source of pressurized air is prevented from passing axially along the length of the plunger and outwardly through the vent port. The constant entry of the O-ring into a sealing relation with the bore progressively induces wear of the O-ring, whereby after a relatively limited duty sequence a leakage path developes about the O-ring, necessitating disassembly of the valve and replacement of the O-ring or, more usually, discarding of the valve and substitution of a new valve.
A second area of premature valve compromise inherent in prior art devices occurs at the entrance of the supply port to the valve. In valve constructions heretofore known and in the valve of the instant invention, the supply port, in the normal position, is blocked by a sealing member. In the course of the initial movements of the plunger from the normal to the charging position thereof, after the above described O-ring sealing action is effected, a distal end of the plunger unseats the seal component from its blocking relation of the supply port.
In the past, however, plungers have not been provided with means for accurately guiding the same to assure a precise axial movement thereof, with the result that tilting of the plunger causes the distal end to scrape either against the valve seat at the supply port or to engage against the supply port seal in an uncontrolled manner. The resultant gouging of the seat or of the sealing member has resulted in the creation of a leakage path, whereby air is permitted to pass through the supply port in all operating conditions of the valve. Obviously, such action is wasteful of energy and often interferes with the effective operation of the air controlled device.
Further deficiencies of known valve devices include back blast or venting through the actuator button or mechanism, long prestroke, tendency to chatter, and the provision of a restricted flow path from the load to the atmosphere.